The dopamine transporter (DAT) has been identified as the principal brain receptor site previoiusly correlated with the rewarding and euphoric properties of cocaine. Euphoric responses to rapid administration of cocaine can be much more prominent than those that follow slower rates of administration. In previous FYs, investigators in this Branch have found that activators of protein kinase C (PKC) modulate dopamine transport in transiently-expressing COS cells. In this FY, we have followed previous observations that identified DAT as a phosphoprotein, and identified predominant serine phosphoacceptor sites in phosphoamino acid analyses. Studies of site directed mutants in potential phosphoacceptor sites identify no single residue as a sole site. These data increase evidence that PKC activation enhances levels of DAT phosphorylation at multiple serines, and makes phosphorylation an increasingly-strong candidate mechanism for rapid adaptations in dopaminergic systems relevant to cocaine-induced euphoria.